Rational Construction of Breathing Metal–Organic Frameworks through Synergy of a Stretchy Ligand and Highly Variable π–π Interaction

The synergy of a stretchy ligand and highly variable π-π interaction has been proposed as a rational strategy for the construction of breathing metal-organic frameworks (MOFs). Based on this strategy, a breathing MOF, {[Cd₂(AzDC)₂(TPT)₂](DMF)₃} _n, was successfully constructed with stretchy 4,4'-diazene-1,2-diyldibenzoate acid (H₂AzDC) and 2,4,6-tris(4-pyridyl)triazine (TPT) as a source of the π-π interaction. The MOF features structure transformation upon stimulation with solvent guests and varied temperatures, which is straightforwardly characterized by single-crystal structures. Moreover, the solvent-free framework shows breathing behaviors in response to light hydrocarbon (C₂H₄, C₂H₆, C₃H₆, and C₃H₈) sorption, which was verified by stepwise sorption isotherms and in situ powder X-ray diffraction. Additional investigation of the sorption selectivity of C3/C2 systems indicated that the selectivity can be regulated by the modulation of the dynamic breathing behaviors, which can be used for the selective separation of C3/C2 light hydrocarbons.